TypeError: Error #2007: Parameter listener must be non-null.

I've searched the forums and all over the web and have not found an answer.  I don't know why I get this error.  It's extremely simple at the moment, starting the app.  It was working when I had all the functions not in an object.  Any help would be greately appreciated.

TypeError: Error #2007: Parameter listener must be non-null.
    at flash.events::EventDispatcher/removeEventListener()

$(document).ready(function() {
    MyApp.init();
});

var MyApp = {
    prefsFile: '',
    prefsXML: '',
    stream: '',
   
    init: function() {
        window.nativeWindow.addEventListener(air.Event.CLOSING, this.windowClosingHandler);
        this.prefsFile = air.File.applicationStorageDirectory;
        this.prefsFile = this.prefsFile.resolvePath("preferences.xml");
        this.readXML();
    },
   
    readXML: function() {
        this.stream = new air.FileStream();
       
        if (this.prefsFile.exists) {
            this.stream.open(this.prefsFile, air.FileMode.READ);
            this.processXMLData();
        } else {
            this.saveData();
        }
    },
   
    processXMLData: function() {
        this.prefsXML = this.stream.readUTFBytes(this.stream.bytesAvailable);
        this.stream.close();
        var domParser = new DOMParser();
        this.prefsXML = domParser.parseFromString(this.prefsXML, "text/xml");
        var windowState = this.prefsXML.getElementsByTagName("windowState")[0];
        window.moveTo(windowState.getAttribute("x"), windowState.getAttribute("y"));
    },
   
    saveData: function() {
        this.createXMLData();
        this.writeXMLData();
    },
   
    createXMLData: function() {
        var cr = air.File.lineEnding;
           
        this.prefsXML =   "<?xml version='1.0' encoding='utf-8'?>" + cr
            + "<preferences>" + cr
            + "    <windowState" + cr
            + "        x = '" + window.screenLeft.toString() + "'" + cr
            + "        y = '" + window.screenTop.toString() + "'" + "/>" + cr
            + "    <saveDate>" + new Date().toString() + "</saveDate>" + cr
            + "</preferences>";
    },
   
    writeXMLData: function() {
        this.stream = new air.FileStream();
        this.stream.open(this.prefsFile, air.FileMode.WRITE);
        this.stream.writeUTFBytes(this.prefsXML);
        this.stream.close();
    },
   
    windowClosingHandler: function(e) {
        e.preventDefault();
        window.nativeWindow.removeEventListener(air.Event.CLOSING, this.windowClosingHandler);
        this.saveData();
        air.NativeApplication.nativeApplication.exit();
    }
};